The subject of this invention is a top roller-carriage placed in front of the needle and matching the usual bottom carriage in a sewing machine.
Sewing machines, usually equipped with a bottom jaw-carriage, can be equipped also with a top jaw-carriage or roller-carriage, particularly if these machines are intended to assemble superimposed work layers with matched edges.
The top carriage-roller is set in action with a unidirectional intermittent motion by means which change the rotary motion of the main shaft into the intermittent motion synchronous with the carriage movement of the bottom jaw.
We have found that, to get perfect synchronism in advancing two layers of work to be sewn together and to forestall moments when one layer rotates and the other does not, the top carriage-roller must function ahead of the needle and press on the needle plate in the zone between the two parts of the jaw. For this purpose the same applicant has invented a top carriage in which the roller is positioned in front of the needle and the kinematic motion giving the roller a unidirectional intermittent movement that includes: the means which change and transfer the rotary movement of the main shaft of the machine into a unidirectional intermittent movement derived from a shaft positioned in back of the machine behind the sewing mechanisms; a first belt transmission supported by an arm perpendicular to the carriage and in back of the machine, a second belt transmission supported by an arm that transfers the intermittent movement from the back part to the front part of the machine and that is set above the sewing mechanisms; a third belt transmission that transfers the intermittent movement to the roller placed in front of the needle.
The second and third belt transmissions that completely cover the needle and the zone of the pressure foot, can rotate simultaneously around a horizontal axis in a vertical plane, so the conveyor roller can adapt itself to thickness changes.
We have found that the carriage briefly referred to before is a considerable encumbrance in the sewing zone; therefore, the use of this machine by an operator who must guide the work with her hands, as close as possible to the sewing mechanisms, is quite infeasible. In fact, machines having the above-mentioned carriage are used only in automatic units of work.
We have noticed the added inconvenience that, with a change in thickness of the work layer, the roller rises rotating in a vertical plane and withdraws from the sewing zone, so the operator is no longer in the ideal zone as close as possible to the needle.